LTC2662

24

Rev 0

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OPERATION

Fault Indicator Pin (FAULT, Pin 30)

The FAULT pin is an open-drain N-channel output that

pulls low when a fault condition is detected. It is released

on the next rising CS/LD edge. The pin is an open-drain

output suitable for wired-OR connection to an interrupt

bus; a pull-up resistor on the bus is required.

Fault Conditions and Thermal Overload Protection

There are four types of fault conditions that cause the

FAULT pin to pull low. First, an open-circuit (OC) condition

on any of the output pins (OUT0 to OUT4) is triggered

when an output channel enters dropout due to insufficient

detection circuit is provided for each of the five DAC cur-

rent output pins.

FR5 provides a detection flag which is set when the die

temperature exceeds 175°C. The overtemperature condi-

tion also forces all five DAC channels to power down and

the open-drain FAULT pin to pull low. FR5 remains set and

the device stays in shutdown until the die cools. Below

approximately 150°C the DAC channels can be returned to

normal operation. Note that a CS/LD rising edge releases

the FAULT pin regardless of the die temperature.

Since any DAC channel can source up to 300mA, die heat-

ing potential of the system design should be evaluated

carefully. FR6, a power-limit protection flag, is provided

to help prevent accidental damage to the current output

device(s). The power-limit fault condition is triggered for

the 200mA and 300mA full-scale current spans when the

and its current output pin (OUTX) is ≥10V.

Finally, FR7 is provided to flag invalid SPI word lengths.

Valid word lengths are 24 bits, 32 bits, and integer mul-

tiples of 32 bits; any other length causes FR7 to set, the

FAULT pin to assert, and the instruction itself to be ignored.

Config Command

The Config command has four arguments—OC, PL, TS

and RD (see Figure 10).

Setting the OC bit disables open-circuit detection (FR0 to

FR4). Likewise, the PL bit disables power-limit protection

(FR6); and the TS bit disables thermal protection (FR5).

Use these options with caution, particularly PL and TS.

The RD bit is used to select external-reference operation.

The REFCOMP pin must be grounded for external reference

use whether the RD bit is set or not.

Power-Down Mode

For power-constrained applications, power-down mode

can be used to reduce the supply current whenever less

than five DAC outputs are needed. When in power-down,

the voltage-to-current output drivers and reference buf-

fers are disabled. The current DAC outputs are put into a

high impedance state. Register contents are not disturbed

during power-down.

Any channel or combination of channels can be put into

power-down mode by using command 0100b in combi-

nation with the appropriate DAC address. In addition, all

the DAC channels and the integrated reference together

can be put into power-down using the Power-Down Chip

command, 0101b. The 16-bit data word is ignored for all

power-down commands.

Figure 10. Config Command Syntax: Open-Circuit Detection Disable (OC), Power Limit Protection

Disable (PL), Thermal Shutdown Disable (TS) and Reference Disable (RD)

CONFIG COMMAND

2662 F10

1

1

1

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

OC

X

PL

TS

RD

0

CONFIG BITS

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